1. Field of the Invention
This invention relates to a protection cover device and a protection-cover-equipped apparatus, each of which opens and closes a front of a photo-taking optical system or the like.
2. Description of Related Art
Some of cameras have a barrier disposed on a front of a lens barrel and arranged as a protection cover to be openable and closable and to protect a lens from being soiled and damaged while the camera is not used for photographing.
The conventional barrier (protection cover) opening-and-closing mechanism is arranged as shown in FIGS. 11, 12 and 13. Referring to these figures, two barriers 101 and 102 are rotatably secured to a base plate (not shown) in such a way as to be rotatable respectively on centers of rotation 101a and 102a. The base plate is disposed on a front of the lens barrel. A light-passing hole 103a is provided in the base plate for forming an optical path. An opening-and-closing ring 104 is mounted on the base plate in such a way as to be rotatable around an optical axis. A driving spring (tension spring) 105 is hooked on a spring peg part 103b of the base plate and is arranged to urge the opening-and-closing ring 104 to rotate clockwise as viewed in FIG. 11.
A rotation stopper 103c is arranged on the base plate to prevent a further clockwise rotation of the opening-and-closing ring 104 when the ring 104 is rotated to a position where the barriers 101 and 102 are opened by the opening-and-closing ring 104.
The barriers 101 and 102 are provided with arm parts 101b and 102b, respectively. Between the opening-and-closing ring 104 and each of the arm parts 101b and 102b, there is hooked an absorption spring (tension spring) 106, which is arranged to urge the barriers 101 and 102 to move in the direction of closing them.
Further, closing stoppers 104a are formed on the opening-and-closing ring 104. When the barriers 101 and 102 are opened, the arm parts 101b and 102b come to abut on the respective closing stoppers 104a, which then prevent the barriers 101 and 102 from closing.
The barrier mechanism configured in the above manner operates as follows. With no power applied to any parts of the barrier mechanism, the opening-and-closing ring 104 is in a state of being completely rotated clockwise by the urging force of the driving spring 105, and the barriers 101 and 102 are in an open state, as shown in FIG. 11.
When a power F (which may be a retracting force of the zoom lens barrel, a rotating force of a focusing motor, or the like) is received from the lens barrel as shown in FIG. 12, the opening-and-closing ring 104 rotates counterclockwise. Then, the closing stoppers 104a rotate also counterclockwise. In association with this rotation, the barriers 101 and 102 rotate in the closing direction to cover the light-passing hole 103a. For covering the light-passing hole 103a, the amount of rotation, i.e., an angle B, of the opening-and-closing ring 104 may be set at an amount sufficient to cause the barriers 101 and 102 to close the light-passing hole 103a by abutting on each other. However, with the degree of finishing precision of various parts, the play of their fitting engagement, etc., taken into consideration, the amount of rotation (the angle B) should be set at an ample amount including some amount of allowance.
The absorbing spring 106 then effectively acts to prevent the ample rotation from exerting any excessive force on the mechanism. In other words, when the amount of rotation of the opening-and-closing ring 104 is too much, the arm parts 101b and 102b of the barriers 101 and 102, which are in contact with the closing stoppers 104a of the opening-and-closing ring 104 in the open state, come a little apart from the closing stoppers 104a in the closed state.
Further, in a case where the barriers 101 and 102 happen to be prevented from rotating in the direction of closing by some impediment such as grains of sand or the like while they are in process of closing, as shown in FIG. 13, the absorbing spring 106 further elongates to permit the counterclockwise rotation of the opening-and-closing ring 104. The absorbing spring 106 thus permits an escaping movement of the opening-and-closing 104 for the barriers 101 and 102, so that the absorbing spring 106 effectively prevents a mechanical disorder from taking place under such a condition.
While a tension spring is used as the absorbing spring 106 in the above-stated case, the use of the tension spring is replaced with use of a torsion spring by hooking it at the center of rotation of the barriers in some case, for example, as disclosed in Japanese Laid-Open Patent Application No. HEI 7-159856.
However, in the case of the barrier mechanism of the type employing the tension spring as the absorbing spring, the absorbing spring cannot be disposed within an action area including a barrier moving part in the direction of a photo-taking optical axis. The use of the tension spring thus imposes a limitation on the structural arrangement of the barrier mechanism to necessitate use of a wide space for it.
Further, since the tension spring requires a space for its coil diameter in the direction of the optical axis, this causes an increase in the direction of thickness of the barrier mechanism.
Meanwhile, the barrier mechanism of another type using a torsion spring as the absorbing spring requires a thickness space, as a coil part, for its number of turns on the reverse side of the barrier mechanism. The coil part also causes an increase in the direction of thickness of the barrier mechanism. Besides, in order to make the spring force of the torsion spring efficiently act on each of the barriers, its coil part must be disposed in the center of rotation of the barrier. These requirements impose limitations on the design and the structural arrangement of the barrier mechanism.
It is conceivable to reduce the necessary space by arranging the tension spring or the torsion spring to have a smaller coil diameter or a less number of turns. Such arrangement, however, tends to cause the spring to be used beyond the limit of elasticity within a normal range of action and thus hardly enables the spring to adequately fulfill its function.